Low intensity radiant infrared heating systems of the type described above are preferred in many applications because of the high thermal heating efficiency and effective utilization which can be realized. An advantage of the radiant energy system is the fact that it is not used to directly heat the air of the enclosure in which it is placed; rather, the infrared source emits radiation which is absorbed by humans, animals, plants in the heated area. In addition, a concrete floor under an infrared emitter will absorb frequencies within the emission spectrum of the system and thereafter release thermal energy to make the enclosure more comfortable and healthful for its inhabitants on an economical basis. Low intensity infrared systems have the further advantage of high directionality and the ability to be placed where needed, thus increasing effective utilization.
It is unavoidable, however, that such heating systems suffer from inefficiencies due to what have previously been perceived as necessary operating conditions. I have found that it is not necessary to compromise efficiency on the basis of certain heretofore accepted operating conditions and this discovery forms the basis for one aspect of my invention hereinafter described.
The hot gaseous effluent of low intensity infrared radiant energy heating systems is typically highly acidic and, therefore, corrosive to system components when cooled to dew point or condensation levels; i.e., the odor producing additives, for example, in natural gas include sulfur and the oxidation of sulfur in the presence of moisture produces sulfuric acid. Accordingly it is generally believed necessary to operate the system with a sufficiently high exhaust temperature so as to avoid condensation of the corrosive constituents of the effluent at or near the exhaust end of the system. High exhaust temperatures can be readily equated with reduced efficiency. As an example, prior art systems may have a temperature adjacent the burner of 1000.degree. F. and an exhaust temperature of 300.degree. F.
The prevalent design principle of the industry is based on the assumption that a heating system must be designed for the worst case condition; i.e., the most extreme difference between outside air temperature and the desired temperature of the heated enclosure. In Detroit, for example, the average annual temperature is in the area of 40.degree. F. and a heating system, on the average, must only be capable of producing a 25.degree. temperature rise in order to produce comfortable temperatures of 65.degree. F. for human inhabitants or to meet certain codes. However, the typical heating system is designed for an outside air temperature of -10.degree. F. and is thus capable of an overall temperature increase of at least 80.degree.. When such a system is activated or switched on the exhaust temperature is initially room temperature as all of the heat produced by the oxidation of fuel goes into heating up the physical components of the heating system. Since the heating system is substantially entirely within the enclosure, and ultimately gives up all of its heat to the enclosure, albeit not always effectively, the initial thermal efficiency of the activated system is near 100%. As the system heats up the exhaust temperature also goes up and more and more heat is simply thrown away at the exhaust end. Efficiency goes down correspondingly. The understanding of this relationship forms the basis for one aspect of the invention hereinafter described.
Another aspect of the invention involves the design of a control system, preferably of the type which includes a microprocessor with a programmable memory, for controlling a plurality of system operating parameters and sequencing certain events for maximum safety and effectiveness.